Lesson 10: Viruses of the Nervous System

Viruses that affect the nervous system can cause a range of diseases in both veterinary and medical contexts.

A. Veterinary Viruses of the Nervous System

1. Family: Rhabdoviridae
   • Genus: Lyssavirus
   • Virus: Rabies virus
   • Host: Mammals (domestic animals, wildlife)
   • Transmission: Bite or scratch from infected animals (saliva)
   • Pathogenesis: Enters through wounds, travels along peripheral nerves to the central nervous system (CNS), replicates in neurons, causing encephalitis.
   • Clinical Signs: Aggression, fearfulness, paralysis, hypersalivation, difficulty swallowing, seizures, coma.
   • Prevention: Vaccination of pets, wildlife control, post-exposure prophylaxis with rabies vaccine and immunoglobulin.
2. Family: Caliciviridae
   • Genus: Vesivirus
   • Virus: Feline calicivirus (FCV)
   • Host: Cats
   • Transmission: Direct contact with infected cats, contaminated surfaces.
   • Pathogenesis: Virus infects the respiratory and oral mucosa; can spread to the nervous system in severe cases.
   • Clinical Signs: Oral ulcers, respiratory symptoms, neurological signs (incoordination, seizures) in rare cases.
   • Prevention: Vaccination, hygiene, and isolation of sick animals.
3. Family: Paramyxoviridae
   • Genus: Morbillivirus
   • Virus: Canine distemper virus (CDV)
   • Host: Dogs, ferrets, wildlife (raccoons, skunks)
   • Transmission: Aerosolized respiratory secretions, direct contact with infected animals.
   • Pathogenesis: Initially infects respiratory epithelium, spreads to lymphatic tissues, and later affects the CNS.
   • Clinical Signs: Fever, respiratory signs, gastrointestinal symptoms, neurological signs (seizures, tremors, ataxia).
   • Prevention: Vaccination, hygiene, and isolation of infected animals.
4. Family: Picornaviridae
   • Genus: Enterovirus
   • Virus: Porcine enterovirus (e.g., porcine encephalomyelitis virus)
   • Host: Pigs
   • Transmission: Fecal-oral route, contaminated feed/water.
   • Pathogenesis: Infects intestinal tract and can spread to CNS, leading to neuronal degeneration.
   • Clinical Signs: Neurological signs (tremors, ataxia, paralysis), diarrhea, poor growth.
   • Prevention: Good hygiene practices, biosecurity measures.

B. Medical Viruses of the Nervous System

1. Family: Rhabdoviridae
   • Genus: Lyssavirus
   • Virus: Rabies virus
   • Host: Humans, mammals (dogs, bats, etc.)
   • Transmission: Bite or scratch from an infected animal (saliva).
   • Pathogenesis: Enters the body through wounds, travels along nerves to the CNS, causes encephalitis.
   • Clinical Signs: Fever, confusion, hydrophobia, paralysis, seizures, death due to respiratory failure.
   • Prevention: Vaccination of pets, post-exposure prophylaxis, public awareness campaigns.
2. Family: Togaviridae
   • Genus: Alphavirus
   • Virus: Eastern equine encephalitis virus (EEEV)
   • Host: Humans, horses, birds (reservoirs).
   • Transmission: Mosquito bites.
   • Pathogenesis: Virus infects and replicates in the CNS, leading to encephalitis.
   • Clinical Signs: High fever, headache, seizures, neurological deficits, can lead to death.
   • Prevention: Vaccination for horses, mosquito control measures.
3. Family: Flaviviridae
   • Genus: Flavivirus
   • Virus: West Nile virus (WNV)
   • Host: Humans, birds, horses, other mammals.
   • Transmission: Mosquito bites.
   • Pathogenesis: Virus enters bloodstream, crosses the blood-brain barrier, causes inflammation and neuronal damage.
   • Clinical Signs: Fever, headache, confusion, muscle weakness, flaccid paralysis, seizures.
   • Prevention: Mosquito control, vaccination for horses.
4. Family: Herpesviridae
   • Genus: Simplexvirus
   • Virus: Herpes Simplex Virus (HSV)
   • Host: Humans
   • Transmission: Direct contact with infected secretions, sexual contact, vertical transmission during birth.
   • Pathogenesis: Virus can establish latency in neurons and reactivate, leading to encephalitis.
   • Clinical Signs: Fever, headache, seizures, confusion, focal neurological deficits in cases of herpes simplex encephalitis.
   • Prevention: Antiviral medications, safe sex practices, maternal screening during pregnancy.
5. Family: Picornaviridae
   • Genus: Enterovirus
   • Virus: Enterovirus D68 (EV-D68)
   • Host: Humans (primarily children)
   • Transmission: Respiratory droplets, contaminated surfaces.
   • Pathogenesis: Primarily affects respiratory tract but can invade CNS leading to acute flaccid myelitis.
   • Clinical Signs: Respiratory symptoms, muscle weakness, paralysis.
   • Prevention: Hygiene practices, avoidance of close contact during outbreaks.

These viruses demonstrate the importance of understanding their transmission routes, clinical presentations, and prevention strategies. In both veterinary and medical contexts, vaccination and hygiene play critical roles in preventing outbreaks and protecting the health of affected populations.